Personal finance is a detailed analysis of financial flows at various points in time. For example, we may receive employment income today, but have to pay college tuition fees next year. Mortgage payments, interest earned, insurance premiums, and numerous other financial flows are recurring events that repeat at monthly or yearly intervals. Because these involve several time periods, we have to ask "What role does time have in these financial calculations?".

We know that if we deposit money in a bank account we will receive interest. Because of this, we prefer to receive money today rather than in the future. Money we receive today is more valuable to us than money received in the future by the amount of interest we can earn with the money. This is referred to as the time value of money. To adjust for this time value, we use two simple formula. The present value formula is used to discount future money streams, that is, to convert future amounts to their equivalent present day amounts. The future value formula is used to convert today's money into the equivalent amount at some time in the future.

All personal financial planning done by professionals uses these time value formula, as well as several more complicated variants of the formulas. To ignore the role that time plays in financial planning is to ignore one of the most important principles of personal finance.

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